Kinda confused about the question. Are we listing popular idols (already have a lot movies and fans) or fresh idols (only a few videos and relatively unknown) or both?
I'll just list the fresh ones since we don't have a topic for that yet (listed in order of freshness):
Mio Ooshima: Debut 2015-08-21. 2 videos released.
I really enjoyed her performance in APAA-323. She still has that new girl shyness and a cute smile that reminds me of Mika Osawa. Can't quite put my finger on it but something just stands out about her.
Uta Sachino: Debut 2015-07-10, 9+ videos released.
She reminds me of Karen Haruki except even cuter and softer. I didn't think that was possible. Shes only been in the game for less than 3 months, and she already has over 9 videos. Given her current pace she seems to be gaining popularity very fast.
Moka Teni: Debut 2015-07-09, 3 videos released.
Cute innocent face and smile. She doesn't seem slutty at all which I think is her appeal. And all her videos are bartender theme, if that is your thing.
Yui Shimasaki: Debut 2015-06-06, 3 videos released.
Another cute, innocent looking girl except unlike Moka her videos seem to be getting more and more hardcore. In only her 3rd video she has already done interracial! High hopes for her.
Nanami Tahara: Debut 2015-05-22, 6+ videos released.
Her debut video (LOVE-165) was a bukakke gangbang! Last person I can remember who did that was Miki Uehara and she turned out fantastic. Her newer stuff is getting more and more debauched. High hopes for this one as well.
Mitsu Satou: Debut 2015-02-05, 13+ videos released.
I don't think anyone really paid much attention to her until her gokkun video with Knights Visual (KV-158). In that video she showed what a great cum swallower she is. If she demonstrates that talent more I think she would be very popular but she seems to be more focused on cosplay fetish.
Mizuki Inoue: Debut 2014-08-01. 15+ videos released.
Her debut was over a year ago but, it seems like she's only really starting to get noticed after her anal video (MUM-178) was released earlier this month. Based on her performances, I feel like she could be the next Rina Hatsume.